Refractory metal contacts and methods of manufacture



Oct. 22, 1963 E. B. GORMAN REFRACTORY METAL CONTACTS AND METHODS OF MANUFACTURE Filed Sept. 23. 1958 INVENTOR Burnout; 8. GOEMHN ATTORNEY 3,107,418 REFRACTORY METAL CONTACTS AND METHGDS OF MANUFACTURE Edmond B. German, Campbell, Calif., assignor, by mesne assignments, to McGraw-Edison Company, Elgin, 11].,

a corporation of Delaware Filed Sept. 23, 1958, Ser. No. 762,854 1 Claim. (Cl. 29-182.3)

The present invention relates to the mounting of refractory metal contacts.

In large oil circuit breakers, a common form of moving contact includes a bar of metal of high conductivity, such as copper, bearing a refractory metal arcing contact as of silver tungsten. In opening of the contacts, particularly when carrying short-circuit current, the silver tungsten arcing contact is subjected to severe conditions during the quenching of the arc. During the closing of the contacts the arcing tip is also subjected to severe treatment including mechanical impact stresses resulting from the characteristic high speed of the closing.

An object of this invention is to provide a novel form of rugged arcing contact to withstand the operating conditions more effectively and a further object is to provide a novel method of assembling of refractory metal arcing contacts to the supporting conductors. It will be understood that the arcing tip on the moving contact cooperates with a similar relatively stationary companion arc tip and that the novel contact structure and method (described below in connection with the moving contact) also have broad application to the stationary arcing tip structure and method of manufacture.

The nature of the invention will be better appreciated and further details and features of novelty will be apparent from the following description of an illustrative embodiment of the invention shown in the accompanying drawing. In this drawing:

FIG. 1 is a fragmentary lateral view of typical moving and stationary contacts of an oil circuit breaker in which the present invention has special application; and

FIG. 2 is an enlarged cross-section of the end of the moving contact appearing in FIG. 1.

Referring now to the drawing, a stationary contact assembly including resiliently supported contact fingers 12 and 14 are shown supported on a tube 16 of insulation. A curved rod 18 bearing an arcing tip 20 engages silver inserts 22 in the stationary contact fingers 12 and 14 when the circuit breaker is closed. Rod 18 is shown as being a form of a circular are that is supported on the center of its curvature on a shaft (not shown) that pivots about an axis perpendicular to the plane of the drawing in carrying the moving contact between closed and open positions. Members 18 and 20 are advantageously of square cross-section; and an additional pair of resilient contact fingers (not shown) like contact finger 12 are usually provided for engaging the remaining two lateral surfaces of the moving contact 18-20.

In operation the moving contact is swung clockwise away from the stationary contact 10, an are being formed between arcing tip 20 and a similar refractory metal arcing tip 24 of contact 14. During reclosing of the contacts the moving contact is swung counterclockwise at high speed with considerable impact when the moving contact tip 20 strikes arcing tip 24 of stationary contact finger 14 as Well as the other contact fingers. There is consequently a considerable stress imposed on the junction between the refractory metal tip 20 and high conductivity metal support 18.

These elements are united as follows. In FIG. 2 metal support 18 of copper is shown united to refractory metal tip 20 as of silver-tungsten by means of an inter- 3,167,418 Patented Get. 22, 1963 posed layer 26 of silver and with a thin layer 28 of a brazing metal alloyed to the opposed faces of member 18 and inside wall 26 of the hollow thimble-like arcing contact 20. In particular, member 18 is seen to include a projection 18a that extends into the hollow bounded by wall 26 on the inside of contact 20.

A preferred method of forming this unit includes the following steps. A preform of tungsten powder or the like is compacted in the shape shown in the drawing and designated 20. Other suitable refractory materials may be included with or in place of the tungsten powder. This compacted preform may be placed in a mating cavity in a crucible as of graphite and the prefrom filled with silver, advantageously including any desired trace impurities for improving the wetting action of the molten silver. The cavities in the crucible should preferably be of sufficient depth to allow for an excess bulk of silver above the preform. This assembly is then fired as in a hydrogen or other reducing atmosphere so as to cause the silver to melt and completely fill the hollow preform and to thoroughly impregnate the preform. Advantageously as illustrated a substantial wall thickness will also be built up at the upper end of the preform where subsequently it will be united to the metal support 18. It is evident that the metal of the wall 26 amounts to an integral extension of the same metal that fills the interstices between the compacted refractory metal particles that formed the preform.

After firing and cooling, the unit will have a silver core. This is machined as by boring so as to fit on reduced projection 18a extending integrally from support member 18. The thus formed contact tip is assembled to the support 18-18:: and brazed, using a torch and an appropriate flux and silver solder or the like having a lower melting point than either the copper support 18 or the silver wall 26. The silver solder or alternative brazing material is of limited bulk but flows readily and alloys with the opposing surfaces of metal support 1818a and with the silver that forms the inner wall 26 of the contact tip. The thickness of this wall is substantially greater than the brazing layer so as to be ample for alloying with the brazing material. A bond of greater consistent strength is realized than would be the case if the substantial wall thickness 26 were not provided. The outer contour of members 18 and 20 is square but machined members 18a and 26 are preferably cylindrical. However it is not required that the thickness of wall 26 be uniform; for the inner surface of the preform might very well be corrugated so as to provide a series of ridges and valleys filled with silver. By restricting the amount of silver used in the firing operation to that necessary for thoroughly impregnating the preform and for amply filling the valleys between such inwardly directed ridges in the preform the amount of machining of the bore might be reduced. It is important however that an ample quantity of silver be provided all around and along projection 18a. As an indication of the extent of flow required of the brazing material, the length of the refractory arcing tip shown is of the order of two inches in a particular application.

It is apparent that the foregoing description is illustrative of the exemplary form presently contemplated for achieving the objects of this invention and that those skilled in the art will readily make modifications and varied applications of the foregoing. Consequently the invention should be broadly construed in accordance with its full spirit and scope.

What is claimed is:

A contact element for heavy duty circuit breaker equipment, including (a) a main support member of high conductivity metal,

separated at all points of relative contact by a relatively thick wall of silver, the silver in said Wall being integrally united with and being an extension of the silver in said sintered metal mass, and

(f) a relatively thin layer of metal brazing material securing said silver wall to said main support member at all points of contact, said brazing material having a lower melting point than the silver in said 5 wall and the metal in said main support member.

References Cited in the file of this patent UNITED STATES PATENTS Schwarzkopf Oct. 26, 1937 Kiefier Feb. 27, 1940 Patch et al. Oct. 15, 1946 Rice Feb. 6, 1951 Levi Feb. 16, 1954 Williamson Apr. 19, 1955 

